1. Field of the Invention
The present invention relates to a leveling system for a trailer. More particularly, but not by way of limitation, the present invention relates to a bed leveling system for a load hauling trailer to stabilize a payload and mitigate torsional stress on the trailer due to differences in the cross slope between the front and rear of the trailer.
2. Background of the Invention
Generally speaking, trailers for hauling a payload are well known in the art. Typically such trailers are connected to a tractor, commonly known as axe2x80x9csemi tractorxe2x80x9d, through a fifth-wheel type connector. Usually such trailers have no provision for leveling the payload while the trailer is being towed. This lack of leveling can cause loads with a high center of gravity to become unstable under certain conditions.
Stability problems can take on an even greater dimension when hauling exceptionally large, heavy loads. Specialty trailers for hauling such loads are well known in the art. Typically these trailers may include a relatively large number of axles to reduce the load per axle to an acceptable level. In a typical arrangement, such trailers include front running gear which includes a fifth wheel connector for attaching the trailer to a tractor for hauling; rear running gear; and a load unit, or bed, suspended by front and rear goosenecks from the front and rear running gear, respectively. The load unit is often configured to support the load fairly close to the ground, sometimes referred to as a xe2x80x9clow boyxe2x80x9d trailer, to provide greater head room when passing beneath overhead obstacles, such as power lines and overpasses. In addition, maintaining the load unit as close as possible to the ground provides improvement in the stability of the load, as well as facilitating loading and unloading of the trailer. Such trailers may be generically referred to as xe2x80x9cdouble gooseneckxe2x80x9d trailers.
As used herein, the term xe2x80x9crunning gearxe2x80x9d is used to describe a combination of jeeps and/or dollies used to support a gooseneck.
Generally speaking, trailer connections may be broadly grouped into connections which are articulated to allow side-to-side rotation between the trailer and the towing vehicle, referred to herein as a xe2x80x9cpivotal connectionxe2x80x9d and connections which do not allow side-to-side rotation referred to herein as a xe2x80x9cmoment connectionxe2x80x9d or xe2x80x9cstructural connectionxe2x80x9d. Thus, a conventional trailer connected to a tractor by a fifth wheel connector would employ a pivotal connection while a double gooseneck trailer could have either type of connection at the front gooseneck and either type of connection at the rear gooseneck.
While the stability of the load is a concern with either type of connection, when moment connections are employed, torsional stresses may be induced in the trailer, or load unit, by unevenness in the road surface (i.e. different cross grade under the front and rear portions of the trailer). Such torsional stresses may be particularly damaging to double gooseneck trailers having moment connections at both the front and rear of the trailer. Cornering is known to compound problems with both the stability of the load and the introduction of unwanted torsional stresses in the load unit.
It is thus an object of the present invention to provide a leveling system for a trailer bed which will level, from side-to-side, at least one end of a trailer to improve the stability of loads having a high center of gravity.
It is still a further object of the present invention to provide a leveling system for trailers designed to haul large, heavy loads which will simultaneously level the front and rear portions of a load unit to improve the stability of payloads having a high center of gravity and to reduce torsional stresses in the load unit and the payload.
The present invention provides a leveling system for trailers of the type used to carry a payload. In one embodiment, the leveling system provides a base member, having a curved upper surface attached to the frame of a trailer and a slide member, having a mating, curved lower surface, attached to the bed of the trailer, or a gooseneck. Preferably, both curved surfaces have the same radius so that the curved surface of the slide member will have substantially full engagement with the curved surface of the base member when the leveling system is assembled. Hydraulic cylinders move the slide relative to the base such that the angle between the axis of the base and the axis of the slide may be controlled to level the bed of the trailer.
The system may be operated manually by providing a manual hydraulic valve to control flow of hydraulic fluid to each cylinder or, alternatively, an electronic level may be provided to automatically actuate electrically operated valves to adjust the hydraulic cylinders to maintain the attitude of the trailer bed.
When the system is installed on a conventional fifth wheel-type trailer having a pivotal connection, the leveling device is preferably located at the rear of the bed. It is also preferable that, in such a configuration, the curvature of the base member and the slide member is such that the center of gravity of the loaded bed remains substantially concentric with the center line of the rear axle.
When the inventive device is included on a double gooseneck trailer, front and rear leveling systems may be provided to reduce torsional stresses on the trailer when the trailer is moved over surfaces where the cross grade under the front running gear differs from the cross grade under the rear running gear. Such a system is particularly advantageous when both goosenecks connect to the front and rear running gear through moment connections.